# This module is useful for people doing workday calculations, as it is 
# often done in finance and accounting. Also useful for programmers who
# are building finance applications for small businesses.


from datetime import date, timedelta

(MON, TUE, WED, THU, FRI, SAT, SUN) = range(7)


# workDaySub takes two date objects that represent a start date and an
# end date. This function returns an integer that represents the number
# of workdays inbetween the two dates given as arguments.

def workDaySub(startDate, endDate):
    whichDays=(MON,TUE,WED,THU,FRI)
    deltaDays = (endDate - startDate).days + 1
    fullWeeks, extraDays = divmod(deltaDays, 7)
    numWorkdays = (fullWeeks + 1) * len(whichDays)
    for d in range(1, 8 - extraDays):
        if (endDate + timedelta(d)).weekday() in whichDays:
            numWorkdays -= 1
    return numWorkdays
    
    
# workDayAdd takes a date object representing the start date and an
# integer representing the number of days you want to add to the 
# start date. This function returns a date object that represents
# the new date in the future; the new date is essentially the start
# date plus the number of days to be added.
    
def workDayAdd(startDate, workDays):
    whichDays=(MON,TUE,WED,THU,FRI)
    weeks, days = divmod(workDays,len(whichDays))
    newDate = startDate + timedelta(weeks=weeks)
    for i in range(days):
        while newDate.weekday() not in whichDays:
            newDate += timedelta(days=1)
    return newDate
        
        
# test workDaySub
begin = date(2012, 12, 1)
end = date(2012, 12, 31)
print workDaySub(begin, end)

# test workDayAdd
origDate = date(2013, 1, 14)
addedDays = 74
print workDayAdd(origDate, addedDays)